Cells having pluripotency, such as ES cells and iPS cells, are undifferentiated cells. Owing to the pluripotency of the undifferentiated cells, the applicability of the undifferentiated cells to regenerative medicine etc. is attracting attention, and research and development regarding the undifferentiated cells now are being carried out eagerly. To this end, it is important to maintain the undifferentiated state of the undifferentiated cells during their culture.
Generally, the undifferentiated cells are cultured according to a culture method using feeder cells such as fibroblasts (so-called “on-feeder culture method”). In this method, feeder cells are cultured beforehand, and undifferentiated cells are then seeded on the feeder cells. Also, in recent years, a culture method without involving the use of feeder cells is developed, which is a so-called “feeder free culture method”. In the feeder free culture method, a serum-free medium is used, for example (Patent Documents 1 to 5, Non-Patent Documents 1 to 14).
However, these known culture methods cannot maintain the pluripotency and the undifferentiated state of the undifferentiated cells sufficiently. For example, in the case of mouse-derived pluripotent stem cells, LIF (Leukemia Inhibitory Factor) is added to a medium as a differentiation inhibitory factor. However, sufficient maintenance of the pluripotency and the undifferentiated state cannot be realized merely by adding LIF. Moreover, for human-derived pluripotent stem cells, effective means for maintaining and/or improving the pluripotency and the undifferentiated state thereof have not been established yet.